L'aigua com a factor clau en l'ús eficient de la radiació per la vegetació terrestre

Un grup d'investigació, liderat pel Centre de Recerca Ecològica i Aplicacions Forestals (CREAF), ha analitzat els factors que influeixen en l'eficiència amb què la vegetació utilitza la radiació per a la captació del carboni atmosfèric en el procés de fotosíntesi. L'ús que les plantes fan de la radiació que reben es troba determinat per variables climàtiques, però la prevalença que les precipitacions tenen sobre altres factors, com la temperatura, ha quedat demostrada gràcies a modernes tècniques d'anàlisi micrometeorològic i al processat de les dades recollides pel sensor MODIS, instal·lat en un satèl lit de la NASA. Els resultats exposats obliguen a reformular algunes de les afirmacions tradicionals sobre el funcionament dels ecosistemes.Un grupo de investigación, liderado por el Centre de Recerca Ecològica i Aplicacions Forestals (CREAF), ha analizado los factores que influyen en la eficiencia con que la vegetación usa la radiación para la captación del carbono atmosférico en el proceso de fotosíntesis. El uso que las plantas hacen de la radiación que reciben se encuentra determinado por variables climáticas, pero la prevalencia que las precipitaciones tienen sobre otros factores, como la temperatura, ha quedado demostrada gracias a modernas técnicas de análisis micrometeorológico y al procesado de los datos recogidos por el sensor MODIS, instalado en un satélite de la NASA. Los resultados expuestos obligan a reformular algunas de las afirmaciones tradicionales sobre el funcionamiento de los ecosistemas

Controles ambientales del crecimiento de alfalfa (Medicago sativa L.) a lo largo de un gradiente climático y edáfico

Druille, Magdalena. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal. Buenos Aires, Argentina.Deregibus, Víctor Alejandro. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal. Buenos Aires, Argentina.Garbulsky, Martín Fabio. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal. Buenos Aires, Argentina.13-23Lucerne is one of the most valuable forage species because of its high productivity and nutritional traits. However, the knowledge of spatio - temporal variability and environmental controls of its growth generated from the simultaneous study of several sites and throughout several years is extremely scarce. Five - year biomass data were analyzed from four rain fed sites located across a climatic and edaphic gradient in Argentina. The aims proposed were to characterize annual and seasonal lucerne growth, to analyze environmental controls of spatial and temporal growth, and to compare water use efficiency (WUE) among sites. Annual growth differed significantly among sites, ranging between 7,514 and 14,262 kg DM/ha. This range at the spatial scale was mainly explained by variations in annual rainfall and WUE among sites. Seasonal growth depended on incident radiation and actual evapotranspiration. Interannual variability of lucerne growth was explained by precipitation occurred during the growing season in the driest sites, on sandy soils with less water retention capacity. Knowing the sources of variability of lucerne growth, would allow developing more efficient livestock management due to less uncertainty on the forage production dynamics

Regional analysis of urban heat islands in Argentina

La urbanización es una de las formas más extremas de cambios en el uso de la tierra y tiene impactos sobre el clima, el agua y la biodiversidad en grandes áreas de todo el planeta. En este trabajo se cuantificaron las islas de calor urbano (ICU) y se relacionaron con características de las ciudades y su entorno a lo largo de gradientes ambientales de la Argentina. Analizamos 55 de las ciudades más grandes del país, ubicadas en 10 ecorregiones, mediante datos satelitales (MODIS) de temperatura de la superficie terrestre, albedo e índices de vegetación (NDVI), y de variables climáticas. La ICU diurna promedio anual de las ciudades argentinas para 2011-2015 fue 0.36±1.99 °C y la nocturna 1.68±0.61 °C. Los principales controles de la intensidad de la ICU fueron el NDVI rural, la precipitación media y la temperatura media durante el día y, en menor medida, la diferencia del albedo durante la noche. Durante el día, algunas ciudades se comportaron como islas de frío urbano (IFU) asociadas a climas áridos o a contextos agrícolas, mientras que durante la noche, todas las ciudades se comportaron como ICU. El efecto atemperador de la vegetación urbana se identificó a partir de la diferencia de NDVI urbano y rural, pero no se observó una relación directa negativa de ICU con NDVI urbano. Los resultados de este trabajo proveen nuevos conocimientos sobre los controles de las ICU y permitiría generar estrategias de desarrollo urbano para mitigar los efectos de la urbanización y mejorar la calidad de vida de la población urbana.Urbanization is one of the most extreme land use changes and has impacts on climate, water and biodiversity in large areas throughout the planet. In this paper, we quantified the urban heat islands (ICU, acronym in Spanish) and its relation to biophysical parameters of the surface of the earth along the main environmental gradients of Argentina. We analyzed 55 of the largest cities in the country, located in 10 ecoregions, using satellite data (MODIS) of land surface temperature, albedo and vegetation indexes (NDVI) and climatic variables. The average annual ICU in the cities for 2011-2015 was 0.36±1.99 °C for the day and 1.68±0.61 °C for the night. The main drivers of the ICU during the day were rural NDVI, mean precipitation and temperature. At night, the main driver was the difference between urban and rural blue albedo. During the day, some cities behaved like urban cold islands (IFU, acronym in Spanish) associated with arid climates or agricultural contexts, while at night, all cities behaved like ICU. The cooling effect of urban vegetation was identified from the difference of urban and rural NDVI, but no direct negative relationship between ICU and urban NDVI was observed. These results provide new insights on the drivers of the ICU and facilitate the generation of urban development strategies to mitigate the effects of urbanization and to improve the quality of life of urban populations.Fil: Casadei, Paula. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal. Cátedra de Forrajicultura; ArgentinaFil: Semmartin, María Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Garbulsky, Martín Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal. Cátedra de Forrajicultura; Argentin

Temporal trends in the Enhanced Vegetation Index and spring weather predict seed production in Mediterranean oaks

The extremely year-to-year variable production of seeds (masting) is an extended plant reproductive behaviour important for forest dynamics and food webs. The dependence of these episodes of massive seed production on recently or long-term photosynthesised carbohydrates, however, remains controversial. In this paper, we explore whether vegetation (tree canopy) changes, detected using EVI as a proxy of leaf area and photosynthetic capacity, can provide a reliable estimation of seed production. To complete this analysis, we also explored the effect of weather both in the trends of EVI and in acorn crop size. To this end, we compared the trends of the EVI and acorn production over 10 years (2000-2009) in five stands of Quercus ilex L. in Barcelona (Catalonia, NE Spain). We found that acorn production was mainly driven by a combination of: i) a minimum initial threshold in the EVI values, ii) an increase in EVI in the 9 ± 4 months prior to reproduction, and iii) appropriate weather conditions (low water stress) during spring. These results indicated, apparently for the first time, that reproduction in masting species could be detected and partly predicted by remotely sensed vegetative indices. Our results suggested that this particular reproductive behaviour in Mediterranean oaks was driven by a combination of two factors, i.e. good and improving vegetation conditions, as shown by a minimum initial threshold and the increase in EVI needed for large seed crops, and the need of wet weather conditions during spring. Moreover, our results fully supported recent studies that have associated short-term photosynthate production with seed production

On the remote sensing of the radiation use efficiency and the gross primary productivity of terrestrial vegetation

Descripció del recurs: el 20 de juny de 2011La captación de carbono por la vegetación es a escala global el flujo más grande de CO2 e influencia en gran medida el funcionamiento de los ecosistemas. Sin embargo, su variabilidad temporal y espacial sigue siendo poco conocida y difícil de estimar. Las técnicas de teledetección pueden ayudar a calcular mejor la producción primaria bruta (GPP) terrestre, que es la expresión a nivel de ecosistemas del proceso de la fotosíntesis. El objetivo principal de esta tesis fue encontrar una manera de estimar la variabilidad espacial y temporal de la eficiencia en el uso de la radiación (RUE) a escala de ecosistema y por lo tanto mejorar la estimación de la GPP de la vegetación terrestre por medio de datos de teledetección. Se abordaron cuatro objetivos específicos. El primero fue analizar y sintetizar la literatura científica sobre la relación entre el Índice de Reflectancia Fotoquímica (PRI), un índice espectral vinculado a la eficiencia fotosintética, y diversas variables ecofisiológicas a través de un amplio rango de tipos funcionales de plantas y ecosistemas. El segundo objetivo fue analizar y sintetizar los datos de la variabilidad espacial de la GPP y la variabilidad espacial y temporal de la RUE y sus controles climáticos para un amplio rango de tipos de vegetación, desde la tundra a la selva tropical. El tercer objetivo fue comprobar si diferentes índices espectrales, es decir, el PRI, el NDVI (Normalized Difference Vegetation Index) y EVI (Enhanced Vegetation Index), derivados del Moderate Resolution Imaging Spectroradiometer (MODIS) son buenos estimadores de la captación de carbono a diferentes escalas temporales en un bosque mediterráneo. El cuarto objetivo fue evaluar el uso de MODIS PRI como estimador de la RUE en un amplio rango de tipos de vegetación mediante el uso de datos sobre la captación de carbono de la vegetación derivados de las torres de covarianza turbulenta. Las principales conclusiones de esta tesis son que hay una coherencia emergente de la relación RUE-PRI que sugiere un sorprendente grado de convergencia funcional de los componentes bioquímicos, fisiológicos y estructurales que afectan la eficiencia de captación de carbono a escala de hoja, de cobertura y de ecosistemas. Al complementar las estimaciones de la fracción de radiación fotosintéticamente activa interceptada por la vegetación (FPAR), el PRI permite mejorar la evaluación de los flujos de carbono a diferentes escalas, a través de la estimación de la RUE. Una segunda conclusión apoya la idea de que el funcionamiento anual de la vegetación es más limitado por la disponibilidad de agua que por la temperatura. La variabilidad espacial de la RUE anual y máxima puede explicarse en gran medida por la precipitación anual, más que por el tipo de vegetación. Una tercera conclusión es que, si bien EVI puede estimar el incremento diametral anual de los troncos, y el PRI puede estimar la fotosíntesis neta diaria nivel de hoja y la eficiencia en el uso de radiación, el papel del NDVI es más limitado como un estimador de cualquier parte del ciclo del carbono en bosques mediterráneos. Por lo tanto, el EVI y el PRI son excelentes herramientas para el seguimiento del ciclo del carbono en los bosques mediterráneos. Por último, el PRI derivado de información satelital disponible libremente, presenta una relación positiva significativa con la RUE para un amplio rango de diferentes tipos de bosques, incluso en años determinados, en bosques caducifolios. En general, esta tesis proporciona un mejor entendimiento de los controles espacial y temporal de la RUE y abre la posibilidad de estimar RUE en tiempo real y, por tanto, la captación de carbono de los bosques a nivel de ecosistemas a partir del PRI.Carbon uptake by vegetation is the largest global CO2 flux and greatly influences the ecosystem functions. However, its temporal and spatial variability is still not well known and difficult to estimate. Remote sensing techniques can help to better estimate the terrestrial gross primary production (GPP), that is the ecosystem level expression of the photosynthesis process or the rate at which the ecosystem's producers capture CO2. The main objective of this thesis was to find a way to estimate the spatial and temporal variability of the Radiation Use Efficiency (RUE) at the ecosystem scale and therefore to arrive to more accurate ways to estimate GPP of terrestrial vegetation by means of remotely sensed data. Four specific objectives were addressed in this thesis. The first objective was to examine and synthesize the scientific literature on the relationships between the Photochemical Reflectance Index (PRI), a narrow-band spectral index linked to photosynthetic efficiency, and several ecophysiological variables across a wide range of plant functional types and ecosystems. The second objective was to analyze and synthesize data for the spatial variability of GPP and the spatial and temporal variability of the RUE and its climatic controls for a wide range of vegetation types, from tundra to rain forest. The third objective was to test whether different spectral indices, i.e. PRI, NDVI (Normalized Difference Vegetation Index) and EVI (Enhanced Vegetation Index), derived from the MODerate resolution Imaging Spectroradiometer (MODIS) can be indicators of carbon uptake at different temporal scales by analyzing the relationships between detailed ecophysiological variables at the stand level in a Mediterranean forest. The fourth objective was to assess the use of MODIS PRI as surrogate of RUE in a wide range of vegetation types by using data on carbon uptake of the vegetation derived from eddy covariance towers. The main conclusions of this thesis are that there is an emerging consistency of the RUE-PRI relationship that suggests a surprising degree of functional convergence of biochemical, physiological and structural components affecting leaf, canopy and ecosystem carbon uptake efficiencies. By complementing the estimations of the fraction of photosynthetically active radiation intercepted by the vegetation (fPAR) PRI enables improved assessment of carbon fluxes at different scales, through the estimation of RUE. A second conclusion supports the idea that the annual functioning of vegetation is more constrained by water availability than by temperature. The spatial variability of annual and maximum RUE can be largely explained by annual precipitation, more than by vegetation type. A third conclusion is that while EVI can estimate annual diametric wood increment, and PRI can estimate daily leaf level net photosynthesis and radiation use efficiency, the role NDVI is more limited as a surrogate of any part of the carbon cycle in this type of forest. Therefore, EVI and PRI are excellent tools for vegetation monitoring of carbon cycle in the Mediterranean forests, the first ones we tested in this thesis. Finally, the PRI derived from freely available satellite information was also found to present significant positive relationship with the RUE for a very wide range of different forest types, even in determined years, the deciduous forests. Overall, this thesis provides a better understanding of the spatial and temporal controls of the RUE and opens the possibility to estimate RUE in real time and, therefore, actual carbon uptake of forests at the ecosystem level using the PRI. Keywords carbon cycle, Normalized Difference Vegetation Index, Enhanced Vegetation Index, Photochemical Reflectance Index, primary productivity, photosynthesis, remote sensing, climatic controls, eddy covariance, radiation use efficiency, terrestrial vegetation

Environmental controls of alfalfa (Medicago sativa) growth across a climatic and edaphicl gradient.

Lucerne is one of the most valuable forage species because of its highproductivity and nutritional traits. However, the knowledge of spatio-temporalvariability and environmental controls of its growth generated from thesimultaneous study of several sites and throughout several years is extremelyscarce. Five-year biomass data were analyzed from four rain fed sites locatedacross a climatic and edaphic gradient in Argentina. The aims proposed wereto characterize annual and seasonal lucerne growth, to analyze environmentalcontrols of spatial and temporal growth, and to compare water use efficiency(WUE) among sites. Annual growth differed significantly among sites, rangingbetween 7,514 and 14,262 kg DM/ha. This range at the spatial scale was mainlyexplained by variations in annual rainfall and WUE among sites. Seasonalgrowth depended on incident radiation and actual evapotranspiration. Interannualvariability of lucerne growth was explained by precipitation occurred during the growing season in the driest sites, on sandy soils with less water retention capacity. Knowing the sources of variability of lucerne growth, wouldallow developing more efficient livestock management due to less uncertaintyon the forage production dynamics.Fil: Druille, Magdalena. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal; ArgentinaFil: Deregibus, Victor Alejandro. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal; ArgentinaFil: Garbulsky, Martín Fabio. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Animal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentin

Spectral normalized indices related with forage quality in temperate grasses: scaling up from leaves to canopies

Forage quality is an important regulator of livestock performance also determining the grazing capacity in grasslands and pastures. The objective of this work was to develop spectral normalized indices to accurately predict canopy nitrogen (N), neutral detergent fibre (NDF), and acid detergent fibre (ADF) concentrations and in vitro dry matter digestibility (IVDMD) in three forage species, at two phenological stages and under two fertilization conditions. To select indices with the highest possible independence from canopy structure, we prioritized the selection of indices that were stable at both leaf and canopy scales and evaluated if the best selected indices were correlated with selected leaf and canopy structural traits and leaf water content. All possible normalized indices, based on the reflectance and the first difference reflectance, for the 400–2400 nm spectral range were related through simple regression models with N, NDF, and ADF concentrations and IVDMD. The index that combined the first difference reflectance in the 685 and 1770 nm wavelengths was found to be a potentially useful index to predict canopy N concentration under different field conditions. The best indices selected to predict canopy NDF and ADF concentration and IVDMD, based on the reflectance around 2120–2145 and 2250–2260 nm, had limited application and appeared to be suitable only to identify gross differences in fibre and IVDMD. Future studies should analyse how the best selected indices behave under field lighting conditions and for a wide range of species, phenological stages, and variations in canopy structural traits.Fil: Aguirre Castro Moreno, Paula Haydee. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Garbulsky, Martín Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Photosynthetic light use efficiency from satellite sensors: from global to Mediterranean vegetation

Recent advances in remote-sensing techniques for light use efficiency (LUE) are providing new possibilities for monitoring carbon uptake by terrestrial vegetation (gross primary production, GPP), in particular for Mediterranean vegetation types. This article reviews the state of the art of two of the most promising approaches for remotely estimating LUE: the use of the photochemical reflectance index (PRI) and the exploitation of the passive chlorophyll fluorescence signal. The theoretical and technical issues that remain before these methods can be implemented for the operational global production of LUE from forthcoming hyperspectral satellite data are identified for future research.Fil: Garbulsky, Martín Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Produccion Animal. Cátedra de Forrajicultura; ArgentinaFil: Filella, I.. Consejo Superior de Investigaciones Científicas. Global Ecology Unit; España. Centro de Investigación Ecológica y Aplicaciones Forestales; EspañaFil: Verger, A.. Consejo Superior de Investigaciones Científicas. Global Ecology Unit; España. Centro de Investigación Ecológica y Aplicaciones Forestales; EspañaFil: Peñuelas, J.. Consejo Superior de Investigaciones Científicas. Global Ecology Unit; España. Centro de Investigación Ecológica y Aplicaciones Forestales; Españ

Leaf and stand-level carbon uptake of a Mediterranean forest estimated using the satellite-derived reflectance indices EVI and PRI

Various aspects of global environmental change affect plant photosynthesis, the primary carbon input in ecosystems. Thus, accurate methods of measuring plant photosynthesis are important. Remotely sensed spectral indices can monitor in detail the green biomass of ecosystems, which provides a measure of potential photosynthetic capacity. In evergreen vegetation types, however, such as Mediterranean forests, the amount of green biomass changes little during the growing season and, therefore, changes in green biomass are not responsible for changes in photosynthetic rates in those forests. This study examined the net photosynthetic rates and the diametric increment of stems in a Mediterranean forest dominated by Quercus ilex using three spectral indices (NDVI, EVI and PRI) derived from MODIS sensors. Average annual EVI accounted for 83% of the variability of the diametric increment of Q. ilex stems over a 10-yr period. NDVI was marginally correlated with the diametric increment of stems. This study was the first to identify a significant correlation between net photosynthetic rates and radiation use efficiency at the leaf level using PRI derived from satellite data analyzed at the ecosystem level. These results suggest that each spectral index provided different and complementary information about ecosystem carbon uptake in a Mediterranean Q. ilex forest.Fil: Garbulsky, Martín Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas A la Agricultura; Argentina. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; España. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Produccion Animal. Cátedra de Forrajicultura; ArgentinaFil: Peñuelas, Josep. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; EspañaFil: Ogaya, Roma. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; EspañaFil: Filella, Iolanda. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; Españ

Affecting factors and recent improvements of the photochemical reflectance index (PRI) for remotely sensing foliar, canopy and ecosystemic radiation-use efficiencies

Accurately assessing terrestrial gross primary productivity (GPP) is crucial for characterizing the climate-carbon cycle. Remotely sensing the photochemical reflectance index (PRI) across vegetation functional types and spatiotemporal scales has received increasing attention for monitoring photosynthetic performance and simulating GPP over the last two decades. The factors confounding PRI variation, especially on long timescales, however, require the improvement of PRI understanding to generalize its use for estimating carbon uptake. In this review, we summarize the most recent publications that have reported the factors affecting PRI variation across diürnal and seasonal scales at foliar, canopy and ecosystemic levels; synthesize the reported correlations between PRI and ecophysiological variables, particularly with radiation-use efficiency (RUE) and net carbon uptake; and analyze the improvements in PRI implementation. Long-term variation of PRI could be attributed to changes in the size of constitutive pigment pools instead of xanthophyll de-epoxidation, which controls the facultative short-term changes in PRI. Structural changes at canopy and ecosystemic levels can also affect PRI variation. Our review of the scientific literature on PRI suggests that PRI is a good proxy of photosynthetic efficiency at different spatial and temporal scales. Correcting PRI by decreasing the influence of physical or physiological factors on PRI greatly strengthens the relationships between PRI and RUE and GPP. Combining PRI with solar-induced fluorescence (SIF) and optical indices for green biomass offers additional prospects